The present invention relates to a cathode ray tube (CRT), and more particularly, to a CRT that can increase an electron beam deflection efficiency while maintaining an appropriate atmospheric pressure resistance.
Generally, CRTs include a panel having an inner phosphor screen, a funnel having a cone portion, and a neck having an electron gun therein, that are sequentially connected to each other. A deflection yoke is mounted around the cone portion of the funnel to form horizontal and vertical magnetic fields there. In this structure, electron beams emitted from the electron gun are deflected through the horizontal and vertical magnetic fields from the deflection yoke, and land on the phosphor screen.
Recently, CRTs have been employed for use in highly sophisticated electronic devices such as high definition television (HDTV) and OA equipment.
On the one hand, in these applications, the power consumption of the CRT should be reduced to obtain good energy efficiency and the magnetic field leakage due to power consumption should be reduced to protect the user from harmful electronic waves. In order to meet these requirements, the power consumption of the deflection yoke, which is the major source of power consumption, should eventually be reduced.
On the other hand, in order to realize high brightness and resolution of display images on the screen, an increase in the deflection power of the deflection yoke is needed. Specifically, a higher anode voltage is needed for enhancing the brightness of the screen. A correspondingly higher deflection voltage is needed for deflecting the electron beams accelerated by the increased anode voltage. Furthermore, higher deflection frequency, along with the requirement of increased deflection power, is needed to enhance the resolution of the screen. In addition, in order to realize relatively flat CRTs for more convenient use, wide-angle deflection should be performed with respect to the electron beams. Wide-angle deflection also requires increased deflection power.
In this situation, there are needs for developing techniques for allowing CRTs to retain good deflection efficiency while constantly maintaining or reducing the deflection power.
Conventionally, a technique of increasing the deflection efficiency positions the deflection yoke more adjacent to the electron beam paths. The positioning of the deflection yoke is achieved by reducing a diameter of the neck and a neck-side outer diameter of the funnel. However, in such a structure, the electron beams to be applied to the screen corner portions are liable to bombard a neck-side inner wall of the funnel. Consequently, the phosphors coated on the corresponding screen corner portions are not excited and it becomes difficult to obtain good quality screen images.
In order to solve such problems, it has been proposed that the cone portion of the funnel, around which the deflection yoke is mounted, be formed with a shape where a circle gradually changes into a rectangle from a neck-side of the funnel to a panel-side of the funnel. This shape corresponds to the deflection route of the electron beams. In this structure, the size of the cone portion is minimized so that the deflection yoke can be positioned more adjacent to the electron beam paths.
However, in the above technique, because the cone portion has a substantially rectangular overall shape, atmospheric pressure resistance is reduced at the cone portion. Therefore, a potential explosion problem exists in a glass-bodied CRT due to compression stress working in the horizontal and vertical axis directions and tensional stress working in the diagonal axis direction.
When the cone portion of the funnel is formed with a circular shape, the potential explosion problem is absent in the CRT because of the circular symmetry in stress. In contrast, when the cone portion of the funnel is formed with a rectangular shape, the maximum stress is concentrated on the diagonal side of the cone portion so that the atmospheric pressure resistance is deteriorated, causing the potential explosion problem.
Recently, as computer simulation techniques have been rapidly developed, it has become possible to perform a stress analysis with respect to the funnel. With the aid of such a stress analysis, the stress concentrated portions of the funnel are correctly checked and a stress distribution can be made over the funnel in an appropriate manner.
It is an object of the present invention to provide a CRT which has a funnel cone portion formed with a large thickness at a region ranged from a deflection reference line to an inflection point in a tube axis direction on the basis of a computer simulation technique.
This and other objects may be achieved by a CRT including a panel having an inner phosphor screen, and a funnel having a panel sealing side, a cone portion and a neck sealing side. The panel sealing side of the funnel is sealed to the panel at a phosphor screen-side. A deflection yoke is mounted around the cone portion of the funnel. A neck is sealed to the neck sealing side of the funnel and an electron gun is mounted within the neck. The cone portion of the funnel is formed with a sectional shape where a circle gradually changes into a non-circle from a neck-side of the cone portion to a panel-side of the cone portion.
The cone portion of the funnel has a thickness in a horizontal axis direction and a thickness in a diagonal axis direction, and the ratio of the diagonal thickness to the horizontal thickness ranges from 1.03 to 1.21. The diagonal thickness of the cone portion non-monotonically increases or decreases from the panel sealing side to the neck sealing side and at least one or more maximum thickness values or one or more minimum thickness values are present between the panel sealing side and the neck sealing side.